As communications technologies develop and a requirement of a user on a communications network is ever-increasing, a 5G communications network technology (or referred to as 5th generation mobile communications technology) is being rapidly standardized. A logical concept of a network slice is introduced in the 5G communications network technology. An operator pre-configures a network slice selection policy (network slice selection policy, NSSP) for a terminal. It should be noted that, the terminal may also be referred to as user equipment (user equipment, UE). The pre-configured NSSP includes one or more rules (rule), and each rule associates a third-party application program (application, App) to single network slice selection information (single network slice selection assistance information, S-NSSAI). When the UE needs to use an app, the UE obtains corresponding S-NSSAI through mapping based on the rule in the NSSP, and establishes a protocol data unit (protocol data unit, PDU) session (session) in a network slice corresponding to the S-NSSAI.
However, a case in which an NSSP in a visited public land mobile network (visited public land mobile network, VPLMN) is not configured for the UE may exist. When the UE roams to the VPLMN, the UE has no NSSP in the VPLMN, and consequently cannot determine a network slice in which a PDU session established. Alternatively, the following case may exist: When the UE roams to a VPLMN, the UE obtains an NSSP in the VPLMN, but when the UE needs to use an app of a home public land mobile network (home public land mobile network, HPLMN), the UE cannot find a corresponding rule from the NSSP in the VPLMN, and consequently the UE cannot determine to-be-used S-NSSAI to establish a PDU session.